Soybean seeds represent perhaps the most significant oil seed in the world. Approximately 28% of the world's supply of fats and oils is derived from soybean oil. More than 90% of this soybean oil is used in food products. In the United States, soybean oil is considered to be the major vegetable oil that is produced and consumed. (World Soybean Research Conference III Proceeding, Shibles, R., Editor. 1985)
Soybeans also provide an excellent source of protein. As such, soybeans represent a potential alternative to meat. Tofu and soymilk are the two principal food products derived from soybean seeds. More than one billion people in China and Southeast Asia, it has been stated, rely on tofu as a major food protein source (Proceedings of the International Soya Protein Food Conference, American Soybean Association, p. 35, 1978). Soymilk is similarly an important source for food protein.
Soybean oil contains five different types of fatty acid. These five types of fatty acids are: palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2), and linolenic acid (18:3). Palmitic acid and stearic acid represent the two saturated fatty acids. Palmitic acid averages approximately 11% of the total fatty acids whereas stearic acid averages about 4% of the total fatty acids present in conventional soybean oil.
One application for which soybean oil may be used is the production of plastic fat (e.g., shortening and margarine). Plastic fats are composed of a solid fat matrix, the interstices of which are filled with liquid oil. Solid fats that can crystallize in what is commonly designated as the beta prime (B') form generally have a melting point and other physical properties which are usually desirable for use as a matrix in a plastic fat. In order for a solid fat to stabilize in the B' form for use in a matrix of a plastic fat, it is desirable to have a fatty acid composition of about 15% or more of palmitic acid. The fat may convert from the B' form to the beta (B) form if less than about 15% palmitic acid is present. Although the B form has a higher melting point and greater stability, it has a less desirable physical structure. Accordingly, it would be highly desirable to be able to provide soybean varieties having sufficiently elevated palmitic acid and stearic acid contents so that plastic fat can be produced with the matrix stabilized in the B' form.
Further, the use of soybean oil having a relatively high content of saturated fatty acids should allow production of a more desirable plastic fat. Thus, the higher solid fat content of such soybean oils would be considered more desirable. For example, the use of such a relatively high saturated fatty acid content soybean oil should allow production by interesterification of a plastic fat having substantially higher saturated triglyceride content than can be obtained from soybean oil having the conventional saturated fatty acid content.
It may be desirable for certain applications to utilize soybean oil having relatively high palmitic and stearic acid levels to use, in effect, as a concentrate to be mixed with ordinary soybean oil so as to provide the desired levels of saturated fatty acids. There are potentially other applications for soybean oils having high levels of palmitic acid and stearic acid. For example, such oils might be of interest as a frying oil having increased stability to oxidation compared with ordinary soybean oil. Such oils might also be of interest as raw materials for the production of palmitic and stearic acids and their derivatives.
Palmitic acid levels in soybean seed oil range from 9.3% to 17.4% within the world collection (Erickson et al., Journal of Heredity, Vol. 79, p. 465, 1988). Erickson et al. reports the inheritance of altered palmitic acid percentages in two soybean mutants, C1726 and C1727. The level of palmitic acid in C1727 reportedly averages 17.3% palmitic acid in comparison to 11.5% in the oil of the parent cultivar "Century". Palmitic acid levels reported for soybean seed oil within the world collection are significantly higher than stearic acid levels, which average about 4% of the total fatty acid content.
Applicants' copending application, Ser. No. 445,393, filed Dec. 5, 1989, discloses soybeans exhibiting an endogenous linolenic acid content of less than about 3.0% and a stearic acid content of at least about 20% of the total fatty acid composition. Applicants' copending application, Serial No. 07/461,341, filed Jan. 5, 1990, discloses soybeans exhibiting an endogenous palmitic acid content of at least about 18% of the total fatty acid composition, preferably greater than 20 or even 25%.
Despite the clear need for soybeans having high levels of both palmitic and stearic acids, this objective still remains to be achieved. It would be even further desirable to be able to provide soybeans not only having both high levels of palmitic and stearic acids, but also to have a relatively low linolenic acid content.